Then if there’s evidence of fraud, the GOP should insist that all the mail-in ballots be tossed, since there’s no assurance that they aren’t diluting legitimate votes.
What you are suggesting would not only would disenfranchise the votes of upwards of half the voters who did vote by mail this year, but again would be impossible for all the mail-in ballots already counted by the regular process this year. They have already been separated from any identifying envelope and tossed into the till.